Method for forming nerve graft

ABSTRACT

A method for forming a nerve graft includes the following steps. A carbon nanotube structure is provided. A hydrophilic layer is formed on a surface of the carbon nanotube structure. The hydrophilic layer is polarized to form a polar surface on the hydrophilic layer. A number of neurons are formed on the polar surface of the hydrophilic layer to form a nerve network. The neurons connect with each other.

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201110031597.2, filed on Jan. 28, 2011 andChina Patent Application No. 201110101123.0, filed on Apr. 21, 2011 inthe China Intellectual Property Office, disclosure of which isincorporated herein by reference.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to commonly-assigned applications entitled,“NERVE GRAFT,” filed **** (Atty. Docket No. US39052). “CULTURE MEDIUM,”filed **** (Atty. Docket No. US39057), and “METHOD FOR FORMING CULTUREMEDIUM,” filed **** (Atty. Docket No. US39058).

BACKGROUND

1. Technical Field

The present disclosure relates to a method for forming a nerve graft,especially to a method for forming a nerve graft for guiding injuredneurons to reconnect.

2. Description of Related Art

A nervous system is a complex cellular communication network that ismainly composed of neurons and glial cells (neuroglial cells). Glialcells occupy spaces between the neurons and modulate the neurons'functions. The neurons sense stimuli and transmit this information tothe brain for processing and storage. For example, the neurons receivediverse stimuli from the environment (e.g. light, touch, sound) andtransmit electrical signals, which are then converted into chemicalsignals to be passed on to other cells.

Neurons exist in a number of different shapes and sizes, and can beclassified by their morphology and function. The basic morphology of aneuron includes a cell body and neurites projecting/branching from thecell body towards other neurons. The neurites can also be divided intotwo types by their functions. One is a dendrite, which branches aroundthe cell body and receive signals from other neurons to the cell body.The other is an axon, which branches from the cell body and growscontinually without tapering. The axon conducts the signals away fromthe neuron's cell body. The end of the axon has branching terminals thatrelease neurotransmitters into a gap between the branching terminals andthe dendrites of other neurons. Thus, the information or signal ispropagated.

Neuron damage can lead to neurite degeneration and retraction. If thedamage is severe, breaks in neurites affect signal transmission and thecellular communication between neurons will cease.

What is needed, therefore, is a method for forming a nerve graft whichcan reconnect opposite terminals in broken neurites.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the drawings. The components in the drawings are not necessarilydrawn to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a cross-sectional view of one embodiment of a nerve graft.

FIG. 2 shows a scanning electron microscope (SEM) image of a flocculatedcarbon nanotube film.

FIG. 3 shows an SEM image of a pressed carbon nanotube film.

FIG. 4 shows an SEM image of a drawn carbon nanotube film.

FIG. 5 shows an SEM image of a carbon nanotube structure.

FIG. 6 shows an SEM image of an untwisted carbon nanotube wire.

FIG. 7 shows an SEM image of a twisted carbon nanotube wire.

FIG. 8 is a top view of the nerve graft shown in FIG. 1.

FIG. 9 is a flowchart of one embodiment of a method for forming a nervegraft.

FIG. 10 shows an SEM image of a neuron cultured on a culture substrateof the nerve graft.

FIG. 11 shows an SEM image of the nerve graft shown in FIG. 1, wherein anerve network of the nerve graft is dyed.

FIG. 12 is a cross-sectional view of another embodiment of a nervegraft.

FIG. 13 is a flowchart of another embodiment of a method for forming anerve graft.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1, one embodiment of a nerve graft 100 includes aculture substrate 10 and a nerve network 20 positioned on a surface ofthe culture substrate 10. The nerve network 20 includes a number ofneurons 21. The adjacent neurons 21 connect with each other. The surfaceof the culture substrate 10 has a polarity which attracts a surface ofthe nerve network 20 such that the nerve network 20 can closely adhereto the surface of the culture substrate 10.

The culture substrate 10 includes a carbon nanotube structure 12 and ahydrophilic layer 14 located on a surface of the carbon nanotubestructure 12. The hydrophilic layer 14 has a polar surface 16 locatedaway from the carbon nanotube structure 12. The nerve network 20 ispositioned on the polar surface 16 of the hydrophilic layer 14 such thatthe hydrophilic layer 14 is located between the carbon nanotubestructure 12 and the nerve network 20.

The hydrophilic layer 14 is a hydrophilic environment for growing theneurons 21 of the nerve network 20. The thickness of the hydrophiliclayer 14 is in a range from about 1 nanometer (nm) to about 100 nm.Preferably, the hydrophilic layer 14 has a thickness in a range fromabout 1 nm to about 50 nm. The hydrophilic layer 14 is made frominorganic materials, such as silicon dioxide, titanium dioxide, ironoxide, or any combination thereof. In one embodiment, the hydrophiliclayer 14 is a silicon dioxide layer with a thickness of about 10 nm.

The polar surface 16 of the hydrophilic layer 14 has a polarity suchthat the polarity of the culture substrate 10 can attract the surface ofthe nerve network 20 with opposite affinity. Thus, the culture substrate10 is capable of providing a bio-compatible environment for seeding theneurons 21 and forming the nerve network 20.

The carbon nanotube structure 12 is capable of forming a free-standingstructure. The term “free-standing structure” can be defined as astructure that does not need to be supported by a substrate. Forexample, a free-standing structure can sustain the weight of itself ifthe free-standing structure is hoisted by a portion thereof without anysignificant damage to its structural integrity. Carbon nanotubesdistributed in the carbon nanotube structure 12 defines a plurality ofgaps therebetween. The carbon nanotubes can have a significant van derWaals attractive force therebetween. The free-standing structure of thecarbon nanotube structure 12 is realized by the carbon nanotubes joinedby van der Waals attractive force.

The carbon nanotubes in the carbon nanotube structure 12 can be orderlyor disorderly arranged. The term ‘disordered carbon nanotube filmstructure’ includes, but is not limited to, a structure where the carbonnanotubes are arranged along many different directions such that thenumber of carbon nanotubes arranged along each different direction canbe almost the same (e.g. uniformly disordered), and/or entangled witheach other. The term ‘ordered carbon nanotube film structure’ includes,but is not limited to, a structure where the carbon nanotubes arearranged in a consistently systematic manner, e.g., the carbon nanotubesare arranged approximately along a same direction and or have two ormore sections within each of which the carbon nanotubes are arrangedapproximately along a same direction (different sections can havedifferent directions). The carbon nanotubes in the carbon nanotubestructure 12 can be single-walled, double-walled, and/or multi-walledcarbon nanotubes.

The carbon nanotube structure 12 can include a flocculated carbonnanotube film as shown in FIG. 2. The flocculated carbon nanotube filmcan include a number of long, curved, disordered carbon nanotubesentangled with each other and can form a free-standing structure.Furthermore, the flocculated carbon nanotube film can be isotropic. Thecarbon nanotubes can be substantially uniformly dispersed in theflocculated carbon nanotube film. The adjacent carbon nanotubes areacted upon by the van der Waals attractive force therebetween, therebyforming an entangled structure with micropores defined therein. Sizes ofthe micropores can be in a range from about 1 nm to about 500 nm. Due tothe carbon nanotubes in the carbon nanotube structure 12 being entangledwith each other, the carbon nanotube structure 12 employing theflocculated carbon nanotube film has excellent durability and can befashioned into desired shapes with a low risk to the integrity of thecarbon nanotube structure 12. The flocculated carbon nanotube film, insome embodiments, will not require the use of a structural support dueto the carbon nanotubes being entangled and adhered together by van derWaals attractive force therebetween.

The carbon nanotube structure 12 can include a pressed carbon nanotubefilm. The carbon nanotubes in the pressed carbon nanotube film can bearranged along a same direction or arranged along different directions.The carbon nanotubes in the pressed carbon nanotube film can rest uponeach other. The adjacent carbon nanotubes are combined and attracted toeach other by van der Waals attractive force, and can form afree-standing structure. An angle between a primary alignment directionof the carbon nanotubes and a surface of the pressed carbon nanotubefilm can be in a range from about 0 degrees to about 15 degrees. Thepressed carbon nanotube film can be formed by pressing a carbon nanotubearray. The angle is closely related to pressure applied to the carbonnanotube array. The greater the pressure, the smaller the angle. Thecarbon nanotubes in the carbon nanotube film are substantially parallelto the surface of the carbon nanotube film if the angle is about 0degrees. A length and a width of the carbon nanotube film can be set asdesired. The pressed carbon nanotube film can include a number of carbonnanotubes substantially aligned along one or more directions. Thepressed carbon nanotube film can be obtained by pressing the carbonnanotube array with a pressure head. Alternatively, the shape of thepressure head and the pressing direction can determine the direction ofthe carbon nanotubes arranged therein. Specifically, in one embodiment,a planar pressure head is used to press the carbon nanotube array alongthe direction substantially perpendicular to a substrate. A number ofcarbon nanotubes pressed by the planar pressure head may be sloped inmany directions. In one embodiment, as shown in FIG. 3, if aroller-shaped pressure head is used to press the carbon nanotube arrayalong a certain direction, the pressed carbon nanotube film having anumber of carbon nanotubes substantially aligned along the certaindirection can be obtained. In another embodiment, if the roller-shapedpressure head is used to press the carbon nanotube array along differentdirections, the pressed carbon nanotube film having a number of carbonnanotubes substantially aligned along different directions can beobtained.

In one embodiment, the carbon nanotube structure 12 includes at leastone drawn carbon nanotube film as shown in FIG. 4. The drawn carbonnanotube film can have a thickness of about 0.5 nm to about 100micrometers (∞m). The drawn carbon nanotube film includes a number ofcarbon nanotubes that can be arranged substantially parallel to asurface of the drawn carbon nanotube film. A plurality of microporeshaving a size of about 1 nm to about 500 nm can be defined by the carbonnanotubes. A large number of the carbon nanotubes in the drawn carbonnanotube film can be oriented along a preferred orientation, meaningthat a large number of the carbon nanotubes in the drawn carbon nanotubefilm are arranged substantially along the same direction. An end of onecarbon nanotube is joined to another end of an adjacent carbon nanotubearranged substantially along the same direction, by van der Waalsattractive force. More specifically, the drawn carbon nanotube filmincludes a number of successively oriented carbon nanotube segmentsjoined end-to-end by van der Waals attractive force therebetween. Eachcarbon nanotube segment includes a number of carbon nanotubessubstantially parallel to each other and joined by van der Waalsattractive force therebetween. The carbon nanotube segments can vary inwidth, thickness, uniformity, and shape. A small number of the carbonnanotubes are randomly arranged in the drawn carbon nanotube film andhas a small if not negligible effect on the larger number of the carbonnanotubes in the drawn carbon nanotube film arranged substantially alongthe same direction.

In another embodiment, the carbon nanotube structure 12 can include anumber of stacked drawn carbon nanotube films as shown in FIG. 5.Adjacent drawn carbon nanotube films can be adhered by the van der Waalsattractive force therebetween. An angle can exist between the carbonnanotubes in adjacent drawn carbon nanotube films. The angle between thealigned directions of the adjacent drawn carbon nanotube films can be ina range from about 0 degrees to about 90 degrees. In one embodiment, thecarbon nanotube structure 12 is formed by 30 layers of drawn carbonnanotube films. The angle between the aligned directions of the adjacentdrawn carbon nanotube films is about 90 degrees. Simultaneously, aligneddirections of adjacent drawn carbon nanotube films can be substantiallyperpendicular to each other, thus a plurality of micropores and nodescan be defined by the carbon nanotube structure 12.

Alternatively, the carbon nanotube structure 12 can be formed by anumber of carbon nanotube wires. Thus, one portion of the carbonnanotube wires is arranged substantially parallel to each other andextends substantially along a first direction. In addition, the otherportion of the carbon nanotube wires is arranged substantially parallelto each other and extends substantially along a second direction. Thefirst direction and the second direction can be substantiallyperpendicular to each other. In one embodiment, the carbon nanotube wirecan be classified as untwisted carbon nanotube wire and twisted carbonnanotube wire. Referring to FIG. 6, the untwisted carbon nanotube wireis made by treating an organic solvent to the carbon nanotude filmdescribed above. In such case, the carbon nanotubes of the untwistedcarbon nanotube wire are substantially parallel to the axis of thecarbon nanotube wire. In one embodiment, the organic solvent can beethanol, methanol, acetone, dichloroethane, or chloroform. The diameterof the untwisted carbon nanotube wire is in a range from about 0.5 nm toabout 1 millimeter.

Furthermore, referring to FIG. 7, the carbon nanotube wire can be formedby twisting the carbon nanotube film to form the twisted carbon nanotubewire. Specifically, twisted carbon nanotube wire is formed by turningtwo opposite ends of the carbon nanotube film in opposite directions. Inone embodiment, the carbon nanotubes of the carbon nanotube wire arealigned around the axis of the carbon nanotube spirally.

Referring to FIG. 8, the nerve network 20 includes a number of neurons21. Each neuron 21 includes a cell body 22 and at least one neurite 24branching from the cell body 22. The neurites 24 of adjacent neurons 21connect with each other such that the adjacent neurons 21 can connectwith each other. The neurites 24 of the neurons 21 include dendrites andaxons. Generally, the neurites 24 can grow in any direction from onecell body 22. However if there are a number of cell bodies 22 located onthe surface of the culture substrate 10, the neurites 24 from one cellbody 22 would preferentially extend to adjacent cell bodies 22. Thus,growth directions of the neurites 24 can be guided by positions of thecell bodies 22. In one embodiment, the neurons 21 are hippocampalneurons grown on the surface of the culture substrate 10 including 30layers of carbon nanotube films. Specifically, the culture substrate 10includes a silicon dioxide layer and 30 layers of carbon nanotube films.The hippocampal neurons are grown on a surface of the silicon dioxidelayer.

The culture substrate 10 can define a growth surrounding the neurons 21,thus the nerve network 20 can be formed on the culture substrate 10.Both of the hydrophilic layer 14 and the carbon nanotube structure 12can have good tactility, and nonmetal and bio-compatible properties.Thus, the culture substrate 10 including the hydrophilic layer 14 andthe carbon nanotube structure 12 can be transplanted into a biologicalbody and form a desired shape. Therefore, the shape and a thickness ofthe culture substrate 10 can be designed as a shape and a thickness of awound on the biological body. The neurons 21 of the nerve network 20 cancommunicate with each other, so that if the nerve graft 100 istransplanted into the wound, neurons of the biological body close to thewound will communicate with and connect to the nerve network 20 of thenerve graft 100. Thus, the injured neurons can be reconnected together.An area of the wound can be substantially equal to an area of across-section of the nerve graft, and a distance between an edge of thenerve graft and an edge of the wound can be less than a length of thewound. Therefore, a distance between the neurons of the biological bodyclose to the wound and the nerve network 20 can be less than the lengthof the wound. The less the distance between the neurons of thebiological body close to the wound and the nerve network 20, the shorterthe time of connecting the nerve network 20 and the neurons of thebiological body, and the shorter the wound recovery time. In oneembodiment, the area of the nerve graft is substantially parallel to asurface of the carbon nanotube structure 12, and the area of the nervegraft is greater than 15×15 square millimeters.

Referring to FIG. 9, a method for forming a nerve graft 100 includes thesteps of:

S10, providing a carbon nanotube structure;

S20, forming a hydrophilic layer on a surface of the carbon nanotubestructure;

S30, polarizing the hydrophilic layer to form a polar surface on thehydrophilic layer;

S40, seeding a number of neurons on the polar surface of the hydrophiliclayer; and

S50, culturing the neurons until adjacent neurons connect with eachother to form a nerve network.

In the step S10, the carbon nanotube structure has a number of carbonnanotubes capable of forming a free-standing structure. Thefree-standing structure of the carbon nanotube structure is realized bythe carbon nanotubes joined by van der Waals attractive force. Thecarbon nanotube structure can include at least one carbon nanotube film.The carbon nanotube film can be a flocculated carbon nanotube film asshown in FIG. 2, a pressed carbon nanotube film as shown in FIG. 2, or adrawn carbon nanotube film as shown in FIG. 4. In addition, the carbonnanotube structure can include at least one carbon nanotube wire. Thecarbon nanotube wire can be an untwisted carbon nanotube wire as shownin FIG. 6 or a twisted carbon nanotube wire as shown in FIG. 7. In oneembodiment, the carbon nanotube structure is formed by 30 layers ofdrawn carbon nanotube films. The angle between the aligned directions ofthe adjacent drawn carbon nanotube films is substantially 90 degrees.

In the step S20, the hydrophilic layer is formed on the surface of thecarbon nanotube structure by evaporation or sputtering. The material ofthe hydrophilic layer is hydrophilic. For example, the hydrophilic layeris made from inorganic materials, such as silicon dioxide, titaniumdioxide, iron oxide, or any combination thereof. In one embodiment, thecarbon nanotube structure formed by 30 layers of drawn carbon nanotubefilms is fixed at a frame, and then a silicon dioxide layer is formed onthe surface of the carbon nanotube structure by electron beamevaporation.

In the step 30, the polar surface can be formed on the hydrophilic layerby the steps of:

(a1), providing a supporter;

(b1), placing the carbon nanotube structure having the hydrophilic layeron a surface of the supporter; and

(c1), forming the polar surface on the hydrophilic layer by soaking thecarbon nanotube structure having the hydrophilic layer located on thesupporter.

In step (b1), the carbon nanotube structure can be located on part ofthe surface of the supporter. To decrease a specific surface area of thecarbon nanotube structure and increase an adhesive attraction forcebetween the carbon nanotube structure and the supporter, the step (b1)can further include the following steps: (b11), soaking the carbonnanotube structure located on the surface of the supporter with anorganic solvent; and (b12), evaporating the organic solvent from thecarbon nanotube structure. In one embodiment, the supporter is a plasticpetri dish or an observation dish.

In step (c1), the carbon nanotube structure can be soaked with apolyamino acid solution or a polyetherimide solution to form the polarsurface on the hydrophilic layer. For example, the polyamino acidsolution or the polyetherimide solution can be sprayed on the surface ofthe hydrophilic layer. In one embodiment, to soak the hydrophilic layerwith the polyamino acid solution or the polyetherimide solution, thestep (c1) includes the following steps: (c11), dripping the polyaminoacid solution or the polyetherimide solution on the surface of thehydrophilic layer; and (c12), purging the polyamino acid solution or thepolyetherimide solution from the hydrophilic layer with deionized waterafter the polar surface is formed on the hydrophilic layer. In oneembodiment, the polyamino acid solution is dripped on the carbonnanotube structure for about 10 hours. A concentration of the polyaminoacid solution can be about 20 milligrams per milliliter.

In the step S30, the carbon nanotube structure can be furthersterilized.

Sterilizing the carbon nanotube structure kills all of the bacteriadistributed in the carbon nanotube structure. The carbon nanotubestructure can be sterilized by means of an ultraviolet sterilizationtechnology or a high temperature sterilization technology.

In the step S40, the neurons can be from a mammal, such as a human, amouse, or a cow. In one embodiment, the neurons are hippocampal neuronsfrom a mouse. The neurons can be seeded on the hydrophilic layer byspraying a neuron solution to the polar surface of the hydrophiliclayer, or by dipping the culture substrate into the neuron solution. Inone embodiment, when the polar surface of the hydrophilic layer iscovered by the neuron solution, the neurons in the neuron solution canbe deposited or seeded on the polar surface of the hydrophilic layer.

In step S50, the conditions for culturing the neurons to branch andconnect to other neurons are not limited. The neurons can be culturedunder room temperature and standard atmospheric pressure. The neuronscan also be cultured under a condition similar to a condition in amammal. Referring to FIG. 10, when one of the neurons seeded on thepolar surface of the hydrophilic layer are cultured in a typical cleanroom under room temperature and standard atmospheric conditions forabout 15 days, a number of neurites branch from one of the neurons.

Referring to FIG. 11, if there are a number of neurons located one thepolar surface of hydrophilic layer, the neurites from one neuron wouldpreferentially extend to adjacent neurons. Thus, growth directions ofthe neurites can be guided by positions of the neurons. The neurons canalso be connected by the neurtites to form the nerve network. Cellgrowth factors can be provided by the polar surface of the hydrophiliclayer for culturing the neurons.

Referring to FIG. 12, one embodiment of a nerve graft 200 includes aculture substrate 30 and a nerve network 20 positioned on a surface ofthe culture substrate 30. The nerve network 20 includes a number ofneurons 21. The adjacent neurons 21 connect with each other. The surfaceof the culture substrate 30 has a polarity attracted to a polarity of asurface of the nerve network 20 such that the nerve network 20 canclosely adhere to the surface of the culture substrate 30.

The culture substrate 30 includes a carbon nanotube structure 12, ahydrophilic layer 14, and a polar layer 36. The hydrophilic layer 14 islocated on a surface of the carbon nanotube structure 12. The polarlayer 36 is located on a surface of the hydrophilic layer 14 away fromthe carbon nanotube structure 12. The nerve network 20 is positioned ona surface of the polar layer 36 away from the hydrophilic layer 14. Thehydrophilic layer 14 is located between the carbon nanotube structure 12and the polar layer 36.

The hydrophilic layer 14 makes the carbon nanotube structure 12 ahydrophilic environment for growing the neurons 21 of the nerve network20. In addition, the hydrophilic layer 14 makes the polar layer 36adhere easily to the carbon nanotube structure 12. The thickness of thehydrophilic layer 14 is in a range from about 1 nanometer (nm) to about100 nm. Preferably, the hydrophilic layer 14 has a thickness in a rangefrom about 1 nm to about 50 nm. The hydrophilic layer 14 is made frominorganic materials, such as silicon dioxide, titanium dioxide, ironoxide, or any combination thereof. In one embodiment, the hydrophiliclayer 14 is a silicon dioxide layer with a thickness of about 10 nm.

The polar layer 36 is capable of providing a polarity such that thepolarity of the culture substrate 30 can attract the surface of thenerve network 20. Thus, the culture substrate 30 is capable of providinga bio-compatible environment for seeding the neurons 21 and forming thenerve network 20. A material of the polar layer 36 can be polyaminoacid, polyetherimide, or any combination thereof. The polyamino acid canbe poly-D-lysine (PDL). In one embodiment, the polar layer 36 is a PDLlayer.

Referring to FIG. 13, a method for forming a nerve graft 200 includesthe steps of:

S11, providing a carbon nanotube structure;

S21, forming a hydrophilic layer on a surface of the carbon nanotubestructure;

S31, forming a polar layer on a surface of the hydrophilic layer to formthe culture substrate;

S41, seeding a number of neurons on a surface of the polar layer; and

S51, culturing the neurons until adjacent neurons connect with eachother to form a nerve network.

In the step S11, the carbon nanotube structure has a number of carbonnanotubes capable of forming a free-standing structure. Thefree-standing structure of the carbon nanotube structure is realized bythe carbon nanotubes joined by van der

Waals attractive force. The carbon nanotube structure can include atleast one carbon nanotube film. The carbon nanotube film can be aflocculated carbon nanotube film as shown in FIG. 2, a pressed carbonnanotube film as shown in FIG. 2, or a drawn carbon nanotube film asshown in FIG. 4. In addition, the carbon nanotube structure can includeat least one carbon nanotube wire. The carbon nanotube wire can be anuntwisted carbon nanotube wire as shown in FIG. 6 or a twisted carbonnanotube wire as shown in FIG. 7. In one embodiment, the carbon nanotubestructure is formed by 30 layers of drawn carbon nanotube films. Theangle between the aligned directions of the adjacent drawn carbonnanotube films is substantially 90 degrees.

In the step S21, the hydrophilic layer is formed on the surface of thecarbon nanotube structure by evaporation or sputtering. The material ofthe hydrophilic layer is hydrophilic. For example, the hydrophilic layeris made from inorganic materials, such as silicon dioxide, titaniumdioxide, iron oxide, or any combination thereof. In one embodiment, thecarbon nanotube structure formed by 30 layers of drawn carbon nanotubefilms is fixed at a frame, and then a silicon dioxide layer is formed onthe surface of the carbon nanotube structure by electron beamevaporation.

In the step S31, the polar layer can be formed on the surface of thehydrophilic layer by the steps of:

(a2), providing a supporter;

(b2), placing the carbon nanotube structure having the hydrophilic layeron a surface of the supporter; and

(c2), forming the polar layer on the carbon nanotube structure bysoaking the carbon nanotube structure having the hydrophilic layerlocated on the supporter.

In step (b2), the carbon nanotube structure can be located on part ofthe surface of the supporter. To decrease a specific surface area of thecarbon nanotube structure and increase an adhesive attraction forcebetween the carbon nanotube structure and the supporter, the step (b2)can further include the following steps: (b21), soaking the carbonnanotube structure located on the surface of the supporter with anorganic solvent; and (b22), evaporating the organic solvent out of thecarbon nanotube structure. In one embodiment, the supporter is a plasticpetri dish or an observation dish.

In step (c2), the carbon nanotube structure can be soaked with apolyamino acid solution or a polyetherimide solution to form the polarlayer on the hydrophilic layer. For example, the polyamino acid solutionor the polyetherimide solution can be sprayed on the surface of thehydrophilic layer. In one embodiment, to soak the hydrophilic layer withthe polyamino acid solution or the polyetherimide solution, the step(c2) includes a step of dripping the polyamino acid solution or thepolyetherimide solution on the hydrophilic layer located on the carbonnanotube structure. In one embodiment, the polyamino acid solution isdripped on the carbon nanotube structure for about 10 hours. Aconcentration of the polyamino acid solution can be about 20 milligramsper milliliter.

In the step S31, the carbon nanotube structure having the polar layercan be further sterilized. Sterilizing the carbon nanotube structurehaving the polar surface kills all of the bacteria distributed in thecarbon nanotube structure. The carbon nanotube structure can besterilized by means of an ultraviolet sterilization technology or a hightemperature sterilization technology.

In the step S41, the neurons can be from a mammal, such as human, amouse, or a cow. In one embodiment, the neurons are hippocampal neuronsfrom a mouse. The neurons can be seeded on the polar layer by spraying aneuron solution to the surface of the polar layer, or by dipping theculture substrate into the neuron solution. In one embodiment, when thepolar layer is covered by the neuron solution, the neurons in the neuronsolution can be deposited or seeded on the surface of the polar layer.

In step S51, the conditions for culturing the neurons to branch andconnect to other neurons are not limited. The neurons can be culturedunder room temperature and standard atmospheric pressure. The neuronscan also be cultured under a condition similar to a condition in amammal

Accordingly, the present disclosure is capable of providing a method forforming a nerve graft. The nerve graft including a carbon nanotubestructure has the following benefits. First, the hydrophilic layercovers the surface of the carbon nanotube structure such that the nervegraft has good hydrophilic property. Second, the carbon nanotubestructure is capable of accommodating many different shapes. Third, bothof the hydrophilic layer and the carbon nanotube structure can have goodtactility, and nonmetal and bio-compatible properties. Thus, the nervegraft including the hydrophilic layer and the carbon nanotube structurecan be transplanted into a biological body and form a shape as desired.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Any elements describedin accordance with any embodiments is understood that they can be usedin addition or substituted in other embodiments. Embodiments can also beused together. Variations may be made to the embodiments withoutdeparting from the spirit of the disclosure. The above-describedembodiments illustrate the scope of the disclosure but do not restrictthe scope of the disclosure.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

1. A method for forming a nerve graft, comprising: providing a carbonnanotube structure; forming a hydrophilic layer on a surface of thecarbon nanotube structure; polarizing the hydrophilic layer to form apolar surface on the hydrophilic layer; and forming a plurality ofneurons, connecting with each other, on the polar surface of thehydrophilic layer to form a nerve network.
 2. The method of claim 1,wherein the step of forming the plurality of neurons comprises: seedingthe plurality of neurons on the polar surface of the hydrophilic layer;and culturing the neurons until adjacent neurons of the plurality of theneurons connect with each other, forming the nerve network.
 3. Themethod of claim 1, wherein the step of polarizing the hydrophilic layercomprises: providing a supporter; placing the carbon nanotube structurehaving the hydrophilic layer on a surface of the supporter; and formingthe polar surface on the hydrophilic layer by soaking the carbonnanotube structure having the hydrophilic layer located on thesupporter.
 4. The method of claim 3, wherein the step of polarizing thehydrophilic layer further comprises: soaking the carbon nanotubestructure located on the surface of the supporter with an organicsolvent; and evaporating the organic solvent from the carbon nanotubestructure.
 5. The method of claim 3, wherein the step of soaking thecarbon nanotube structure comprises: dripping the polyamino acidsolution or the polyetherimide solution on the surface of thehydrophilic layer located on the supporter for about 10 hours; andpurging the polyamino acid solution or the polyetherimide solution fromthe hydrophilic layer with deionized water after the polar surface isformed on the hydrophilic layer.
 6. The method of claim 3, wherein aconcentration of polyamino acid solution is about 20 milligrams permilliliter.
 7. The method of claim 3, wherein the polyamino acid ispoly-D-lysine (PDL).
 8. The method of claim 1, wherein the carbonnanotube structure comprises a carbon nanotube film comprising aplurality of carbon nanotubes substantially parallel to a surface of thecarbon nanotube film.
 9. The method of claim 1, wherein the carbonnanotube structure comprises a carbon nanotube film, and the carbonnanotube film is a flocculated carbon nanotube film, a pressed carbonnanotube film, or a drawn carbon nanotube film.
 10. The method of claim1, wherein the carbon nanotube structure comprises a plurality of carbonnanotube films stacked together, and adjacent carbon nanotube films ofthe plurality of carbon nanotube films are combined and attracted toeach other only by van der Waals attractive force therebetween.
 11. Themethod of claim 1, wherein the carbon nanotube structure comprises atleast one untwisted carbon nanotube wire.
 12. The method of claim 1,wherein a material of the hydrophilic layer is selected from the groupconsisting of silicon dioxide, titanium dioxide, iron oxide, and anycombination thereof.
 13. The method of claim 1, wherein a thickness ofthe hydrophilic layer is in a range from about 1 nanometer (nm) to about100 nanometers.
 14. A method for forming a nerve graft, comprising:providing a carbon nanotube structure; forming a hydrophilic layer on asurface of the carbon nanotube structure; forming a polar layer on asurface of the hydrophilic layer away from the carbon nanotubestructure; and forming a plurality of neurons, connecting with eachother, on a surface of the polar layer away from the hydrophilic layerto form a nerve network.
 15. The method of claim 14, wherein the step offorming the plurality of neurons comprises: seeding the plurality ofneurons on the surface of the polar layer; and culturing the neuronsuntil adjacent neurons of the plurality of neurons connect with eachother until the nerve network is formed.
 16. The method of claim 14,wherein the step of forming the polar layer comprises: providing asupporter; placing the carbon nanotube structure having the hydrophiliclayer on a surface of the supporter; and forming the polar layer on thecarbon nanotube structure by soaking the carbon nanotube structurehaving the hydrophilic layer located on the supporter.
 17. The method ofclaim 16, wherein the step of forming the polar layer further comprises:soaking the carbon nanotube structure located on the surface of thesupporter with an organic solvent; and evaporating the organic solventfrom the carbon nanotube structure.
 18. The method of claim 14, whereinthe step of soaking the carbon nanotube structure comprises: drippingthe polyamino acid solution or the polyetherimide solution on the carbonnanotube structure having the hydrophilic layer located on the supporterfor about 10 hours.
 19. A method for forming a nerve graft, comprising:providing a culture substrate; polarizing the culture substrate to forma polar surface on the culture substrate; and forming a plurality ofneurons, connecting with each other, on the polar surface of the culturesubstrate to form a nerve network.